Last updated: February 2, 2026
Genetic evidence related to shared ancestry.
Humans have 46 chromosomes (23 pairs), while chimpanzees, gorillas, and orangutans—our closest living relatives—have 48 chromosomes (24 pairs). This difference presents a challenge for the theory of common ancestry: how could humans have evolved from a common ancestor with these species if we have different chromosome counts?
| Species | Chromosome Count | Closest Living Relative |
|---|---|---|
| Humans (Homo sapiens) | 46 (23 pairs) | — |
| Chimpanzees (Pan troglodytes) | 48 (24 pairs) | Humans (~98.8% DNA similarity) |
| Gorillas (Gorilla gorilla) | 48 (24 pairs) | Humans and chimps |
| Orangutans (Pongo pygmaeus) | 48 (24 pairs) | Humans, chimps, and gorillas |
In 1982, scientists hypothesized that if humans evolved from a common ancestor with the other great apes, two ape chromosomes must have fused to create human chromosome 2, reducing the chromosome count from 48 to 46.
When stained, human chromosome 2 shows banding patterns that match chromosomes 2p and 2q (2p and 2q refer to "chromosome 2-predecessor" and "chromosome 2-subsequent"), which correspond to two separate chromosomes in apes.
Telomeres are distinctive DNA sequences found at the ends of chromosomes. Human chromosome 2 contains telomere sequences in the middle, exactly where the fusion would have occurred. These sequences consist of repeats of TTAGGG, which are characteristic of telomeres but should never be found in the middle of a chromosome unless a fusion has occurred.
Every chromosome has a centromere, a structure that plays a key role in cell division. Human chromosome 2 contains remnants of a second, inactivated centromere precisely where expected if two chromosomes fused.
This hypothesis has been supported through multiple lines of evidence:
A groundbreaking 2025 Nature study4 completed the sequencing of all great ape genomes with unprecedented accuracy. This comprehensive analysis further validated the chromosome 2 fusion by:
Human chromosome 2 is cited as evidence for evolution for several reasons:
Scientists predicted the fusion based on comparative chromosome counts, then found what they expected. This observation is consistent with the predictive framework of evolutionary theory.
There is no functional reason for human chromosome 2 to contain vestigial telomere sequences in the middle or a second inactivated centromere. These features make sense only as remnants of our evolutionary history.
The content and organization of genes on human chromosome 2 correspond to those found on the two separate ape chromosomes, which proponents interpret as evidence of shared genetic history.
Chromosome fusion is a documented genetic process that occurs in many species. This model proposes how humans would have 46 chromosomes if they descended from ancestors with 48 chromosomes.
Human chromosome 2 is presented as an example of a testable evolutionary prediction. The genetic evidence is consistent with the hypothesis that two ancestral ape chromosomes fused to form human chromosome 2, which proponents view as molecular evidence for shared ancestry with other great apes.
This chromosome fusion event occurred after the evolutionary split between humans and chimpanzees, estimated to have happened 4-6 million years ago, and has become fixed in the human population.